IP Communicator is not supported to run on Citrix. This URL lists the requirements which are Windows 2000 and Windows XP:
http://www.cisco.com/en/US/products/sw/voicesw/ps5475/products_data_sheet09186a00801f8e48.html#wp42953
From my understanding the issue faced with making this work is the media termination. I'm not a Citrix expert but I believe the media would terminate on the Citrix server then get pushed out to the client PC. Not only do we need to make sure IP Communicator would work in this mode but there are performance issues that are likely with this model.
I would suggest working with your Cisco account team to create a Product Enhancement Request (PERS) to bring this to the attention of development. Once this is done development can evaluate the possibility of adding this support. I suspect that Citrix will need to be involved as well.
Kevin